Calculation of Radiated Emission from STP Cable by Chain-Parameter-Matrix

Radiated emission from shielded twisted pair (STP) cable was calculated using a chain-parameter-matrix. The series connection of the matrix represented the transmission line inside the shield, and the common-mode (CM) current was obtained by solving the matrix equation. The induction voltage on the outside of the shield was determined from the CM current using the shield’s transfer impedance. The current on the outside of the shield was calculated from this induction voltage. And then, the radiated electric field was calculated from this current. The matrix elements representing the transmission line between conductors and shield were determined from the measurement, and the transfer impedance was also determined from the measurement. The line constants between shield and ground were determined from the theory by assuming the shield as a copper rod. The maximum current on the outside of the shield and the maximum radiated electric field were measured in the frequency range from 30 MHz to 300 MHz, and these were compared to the calculated value. The calculation results of the maximum current intensity were well agreed with the measured value, and the calculation results of the maximum radiated electric-field strength were almost agreed with the measured value.